1. Field of the Invention
The present invention relates to a method for performing storage virtualization; and more particularly, relates to a method for performing storage virtualization which may flexibly expand the storage capacity.
2. Descriptions of the Related Art
In the conventional technologies, the logical drives (LDs)/partitions mapped from a RAID subsystem is presented as physical volumes (PVs) on the host channel for the host to access. The host uses the LBA of the LDs/partitions to access the PVs. Therefore, once the RAID subsystem presents the PVs to the host, it is difficult to change the configuration of the PVs and the associated LDs/partitions. Particularly, it is impossible to reduce the capacity of a PV and the associated LD/partition. Such architecture is subject to some restrictions on the flexibility of the utilization of the RAID subsystem, so the utilization of the storage space of the subsystem is greatly restricted.
For example, assume that a RAID subsystem has a capacity of 800 GB and was originally configured into two 400 GB logical drives, LD1 and LD2, and presented as PV1 and PV2 to the hosts for data access. After a while, it is found that only 100 GB is needed for the utilization of PV1; while the space required for the utilization of PV2 has been consistently increasing and the 400 GB capacity would be insufficient finally. In the conventional technologies, because the configuration of PV1 is unchangeable, only 100 GB capacity thereof will be used while the other 300 GB capacity will be left idle and can not be used. On the contrary, because there is no enough space in PV2, it is necessary to buy some more storage device. It is a waste of resource.
In addition, under some of the conventional data storage system architectures, either data can not be migrated between disk array subsystems or the system performance of data migration therebetween is quite low, which has a negative influence on the utilization flexibility of the resources of and/or the system performance of the data storage system.
Moreover, under some of the conventional data storage system architectures, although data can not be migrated between the disk array subsystems, the disk array subsystems lack RAID function protection, which is not acceptable to the modern information age having high-level data availability demand.
Furthermore, under some conventional data storage system architectures, IO access commands must all be issued through a master storage node in order to be properly executed, even when the data itself which is associated with the IO access commands is not situated in a physical storage device belonging to the node. Under conditions of heavy IO loading, the performance of the system may end up being determined solely by the IO processing power of the master storage node.
Therefore, how to increase the flexibility of utilization of a storage subsystem so as to avoid waste of resources is a big issue in the storage industry.